In conventional color photography, photographic products contain three superimposed units of silver halide emulsion layers, one to form a latent image corresponding to exposure to blue light (blue-sensitive), one to form a latent image corresponding to exposure to green and one to form a latent image corresponding to exposure to red.
During photographic processing, the developing agent reduces the silver ions of each latent image. The thus-oxidized developing agent then reacts in each unit with a dye-forming coupler to produce yellow, magenta and cyan dye images respectively from the recordings in blue, green and red. This produces negative color images.
The reversal photographic products that enable positive images to be obtained comprise the same three superimposed units of silver halide emulsion layers, each of these units containing respectively a yellow, magenta and cyan dye-forming coupler. In the usual photographic reversal process for producing positive color image, after exposure, the reversal photographic product is first developed with a first black-and-white developing bath (latent image development), then it is uniformly exposed and the exposed material is subjected to a second development with a color developing bath. The process is completed by fixing and bleaching the color photographic material.
It is known to replace the uniform exposure by using a chemical fogging agent that is added at the latest to the second development. Compounds known as fogging agents are, for example, boranocarbonates, borohydrides, alkylamino-boranes, tin(II) compounds and thioureas.
One of the drawbacks of some of the fogging agents commonly used is that they are unstable in solution. Some of these compounds cause instability of the color developing bath when carried over from the fogging bath into the color developing bath. The use of some of these compounds is strictly controlled for ecological reasons.
It is therefore an object of the present invention to find a new chemical fogging solution for a photographic reversal process that reduces or substantially obviates the disadvantages of the known chemical fogging agents.